In order for an electron to move to a higher energy level, the photon is absorbed by
the atom. The energy of the photon must be at least enough to raise the electron
from energy level 2 to level 5. The wavelength w can be found by Rydberg's formula
1/w = R(1/L² - 1/U²), where L and U are the lower and upper energy levels, in this
case 2 and 5. R is the Rydberg constant, experimentally found to be10,967,758
waves per meter for hydrogen. So the wavelength w is: 1/w = R(1/4 - 1/25) = 0.21R
The value we get is w = 4.34 * 10**-7 meter, or 434 nanometers and it is absorbed
by the atom to cause the electron to move to the higher energy level.
Answer choice A above is the best choice. Hope this answers your question.
